Seat belts are particularly effective when they are worn by the vehicle occupants closely upon their bodies and slack in the seat belts is minimized. However, as this will cause considerable discomfort to the wearers, retractor devices are widely used with seat belts so as to accommodate the movement of the seat belt wearers by using spring loaded winding spools.
As such a retractor device, the emergency lock retractor device has recently come to be widely used so that the movement of the occupant may not be restrained under normal condition but the winding spool may be locked up instantaneously upon detection of deceleration or rapid pay-out of the seat belt resulting from occurrence of a vehicle crash or a sudden braking to ensure an appropriate level of the tension of the seat belt.
However, such a retractor device merely prevents any further pay out of the seat belt once the winding spool is locked up. If the seat belt is positively retracted to the extent required to remove slack from the seat belt upon detection of a vehicle crash, the occupant will be improved even further.
Based upon such a recognition, various preloader devices have been proposed, such as those disclosed in U.S. Pat. Nos. 4,840,325 and 4,864,086 which improve the capability of the seat belt system to restrain a vehicle occupant by clamping a part of the seat belt paid out from the retractor device and pulling the clamped part towards the retractor device in response to a signal from a deceleration sensor for detecting deceleration greater than a certain level acting upon the vehicle. The disclosure of these patents are incorporated herein by reference.
A vehicle seat is normally mounted on a pair of slide rails extending along the longitudinal direction for permitting the positional adjustment of the seat. Therefore, in order for the seat belt to be in the optimum position irrespective of the adjusted position of the seat, a preloader device is desired to be mounted on the vehicle seat. However, in adjusting the position of the seat or, in case of a walk-in seat, in moving the front seat out of the way for getting into the rear seat, the seat may be moved or stopped abruptly. In particular, when the movement of the seat is abruptly stopped by the engagement of a seat lock mechanism for securing the seat at its adjusted position, an impulsive deceleration acts upon the seat. Therefore, if a preloader device is mounted on such a seat, the deceleration sensor of the preloader device may be erroneously activated. If a deceleration sensor is mounted on the vehicle body separate from the main body of the preloader device to avoid this problem, the assembly work becomes unfavorably complex.